Method and apparatus for regulating centrifugal compressors



' E. BRowN AND A. CARRARD.

METHOD AND APPARATUS FOR REGULATINGA CENTRIFUGAI. COMPRESSORS.

APPLICATION FILED 1AN.,26. 192,0.

V1,40168 .Patented pag.27, 1921. l

. my Y UNITED STATES PATENT oFFice.

ERIC BROWN, OF BADEN, 'AND ALFRED CARRARD, 0F ENNETBADEN, SWITZERLAND, ASSIGNORS T0 AKTIENGESELLSCHAFT BROWN, BOVERI AND CIE., 0F BADEN,

SWITZERLAND.

METHOD AND AP'IARATUS FOR REGULATING CENTRIFUGAL COMLPRESSORS.

Application led January'26, 1920. Serial N. 354,296...

T 0 all whom t may concern,

Be it known that we, ERIC BROWN, a British subject, residing at Baden, Switzerland, aud Amman CARRARD, of Ennetbaden, Swit# zerland, a citizen of the Swiss Republic, have invented certain new and useful Im rovements in Methods and Apparatus for egulating Centrifugal Compressors, of which the following is a specification.

This invention relates to the regulation of centrifugal compressors of the type which aperture, as is well known,

where V1 and V2 are the different volumes and h1 and he the pressures. Y

The amounts delivered for the same wheel are in proportion to its speed:

V, :V2- wt1 m2. and hence A h1 b21-11112 nf, that is, the' amounts delivered increase with the first power of the speed, but the pressures with the square of the same. Points of intersection otseveral pressure-volume curves for diiferent speeds of the compressorl curves for a given speed and two further pressure volume curves 1n whlch the speed of the com ressor is adjusted for constant volume at tlie working point.

Fig. 4 shows diagrammatically an ap'paratus illustrating an application of the invention wherein a by-pass is used for regulating the effect of the compressor output or the adjustment of the guide blades.

Specification of Letters Patent. Patented Dec. 27, 1921.

Fig. 5 is anenlarged view of a guide blade showing its method of setting.

Fig. Gis a modification whereiny the function of the by-pass of Fig. 4 is performed by resilient means.

In the graphic lrepresentation of the working of centrifugal compressors in pressure volume-curves 1t 1s well known'that similar points are caused by variations in the speed of revolution to move in parabolas that have their apex in O' (see the dotted curve in Fig. 1). At a speed of revolution n let A be a working point `orl point of intersection of the pressurecvolume curve 1 with the counter pressure curve OA. On the pressure*` volume curve 2 for a speed of revolution a there will be a working pointA on the same coun-i ter-pressure curve. If the latter is a parabola` passing through O, then A will be a similar point to A, and both points will have a maximum eiiiciency corresponding for instance to the respective speed of revolution these efficiencies will be 'r'jA and 'qlA on4 4 t e efficiency curves *nl and- 'n' 1. These eiliciency curves -are determined in the testlng shop for their corresponding pressure volume curves.

Further from our earlier application for a British patentdated 9 September 1919 and numbered 22,174, it is found that for a given speed ofrevolution, in closing the guide v blade apertures, the pressure volume-curves according to Fig. 2 having the shape 1 will vary and become gradually steeper according lto the curves 2, 3, 4, etc. In such a case the corresponding eiiiciency varies according to the curves nl, u2, n3, Q44

If the counter-pressure curve is a parabola stable delivery, even ifv the delivery were stable, and an eliiciency of only 1;1 could be attained at the working point C. ln position 4 the working point C is obtained low down on the downward branch: the corresponding efficiency n, would be bad. From this it follows that for each counter-pressure c urve -a given position of the guide blades will produce the maximum possible eihciency. f

Since the previously mentioned counter.

blades according to the above stated way,

that is to say, in such a manner that in each case the best possible efficiency is attained irrespectively of the speed of the compressor.

rlhe speed of the compressor may A for in-v stance be adjusted lautomatically for constant volume (Fig. 3, line MN). lf we consider the counter-pressure curves 0 I, 0 il and 0 lll, then for a speed of revolution n for instance, the points D, E, A (analogously to the points A, B, C of Fig. 2) are the working points with. at all times the best positions of the uide blades. rllhe position of the guide bla es remains constant along the counter-pressure curve. Therefore0 if we 'adjust the speed of revolution for constant volume, as above mentioned, then the lworking points will be C, B, A, in which case the guide blades will havethe same positions each time in D andvCJn E and B, and in A. and A. rlhe speed'oi revolution is then different in A, B and C, and is smallest in C.

Fig. 4 illustrates anexample of a preliminary adjusting mechanism which by means of a power-piston adjusts the position of the dif'users a in dependence upon the parabolas l, ll, lill (Fig. 3), and maintains the said position constant along 'a parabola. The guide blades or diffusers a lare rotatably mounted on the one hand by journals g (Fig. 5) and on the other hand they rest on a bolt 7' which is fixed to a rotatable ring s and extends into a slot t of the blade.- The ring s is moved by the power piston b, the position of which is determined by the slide d. e

' The pressure under the piston is adjust. ed with the help of the position of the Iopening slide d which allows lthe oil pressure each counter-'pressure curve.

momes entering lin c and throttled in by a diaphragm to have access to the atmosphere, or throttles said oilpressure more .or less, To a given position of the slide d there belongs a given oil pressure under the piston b, and consequently a determinedl position of this piston as well as of the -guide blades. rlhe position of d is adjusted by means of the rod e which is simultaneously iniiuenced by a volume-piston f and a pressure piston g. In the pipe m leading tothe latter, there is interposed a diaphragm c as a throttling device. z is a bypass which leads around the pressure piston g,'and -has afdierent cross section passage area foreach position' of the piston. F or a given position,`we have equilibrium between f and g. rlhis equilibrium is maintained along a parabola through O, because the air pressureacting upon the piston f as well as upon the piston g, increases with the square of the delivery (law or' proportionality). lf however the counter-pressure curve should vary for i n. stance from l to ll (Fig. 3), the pressure at equal vdelivery will be greater, and the spindle e will moveupward. At this4 higher position of. the piston the cross sectional area of the bypass 71. is greater and the pres- .sure under the piston g will be less effective on account of the throttling at k. The result 'of this will be a new position 4of equilibrium and a diiierent position of the slide d, that is to say, a ldifferent position of the guide blades. Hence it will be seen that the pressure under the piston g is partlyprol0@ portional to the finaly pressure of the compressor and at the same vtime partly dependent' on the relative play of the by-passl L and the diaphragm 7c. By suitably selecting the shape of y the slot, the correct posi- N5- tion of the guide blades can be.obtained for L is the delivery pipe of the centrifugal. compressor; m is Athe ,connecting pipe leading to the pres-A sure piston g; n and o are the pipes leading 1l@ to the volume piston f, fn, indicating the' total energy ando the static energy.

Fig. 6 illustratesan arrangement'similar to F ig. 4, but withl the difference that the bypass It and the diaphragm are replaced U5 by a spring p. Let us assume that for a given counter-pressure parabola l (Fig. 3) for instance all three forces, that is to say, the spring, the pressure-piston and the volume piston are in equilibrium. For another parabola for instance, with constant volume., the, pressure under the pressurepiston is higher (parabola H) the spindle e moves up; but the power of the spring increases; and a new position of equilibrium is thereby established. By correct shaping -of the regulating slide d, the desired posiblades will change automatically as the counter pressure curve varies from parabola to parabola in such a manner that at all- Working points Work Will be done with the smallest possible expenditure of energy of the compressor.

What We claim is l. A regulator for a centrifugal compressor of the type regulated byadjustable guide blades, including a cylinder and piston mechanism for adjusting said guide blades, and automatic means for operating said piston in said cylinder, said means being energized simultaneously by both the pressure' and the volume of the fluid delivered by said compressor.

2. A regulator for a centrifugal compressor of the"` type regulated by adjustable' guide blades, and automatic means including a c linder and piston for adjusting said gui e blades in accordance with the output of said compressor, characterized by the feature that said automatic means is controlled by a preliminary adjusting mechanism which is dependent for its operation on loo-thF the pressure and the volume of the come pressor delivery, said preliminary adjusting l pressor, a cylinder contaming a piston actuated by the volume of the delivery of the compressor, pipes connecting said cylinders With the exhaust orifice of the compressor, a fixed constriction in a pipe. connecting the said pressure piston with the exhaust orifice of the compressor and a passage of variable area of cross section past said-pressure piston for coacting with said fixed constriction, both pistons of the preliminary adjusting mechanism being mechanically .fixed together and coacting With a valve ina pipe connecting the cylinder of the first mentioned automatic means with a source of energy.

In testimony whereof We have signed our names to this specification. p

' ERIC BROWN.

A. CARRARD. 

